“Only load the CSS you need” is the piece I don’t have a go-to tool for. Coverage in Chrome DevTools provides a quick but manual way to identify above-the-fold CSS. Critical, criticalCSS, and Penthouse all look like good options for a build process. [1] [2]

[1]: https://web.dev/defer-non-critical-css/

[2]: https://web.dev/extract-critical-css/